Conventionally, a capacity control valve control apparatus has been proposed that, in order to avoid a rapid pressure increase in a refrigeration cycle circuit, limits an input signal input into a duty ratio control circuit to not have a predetermined duty ratio (see, for example, Patent Literature (PTL) 1).
FIG. 8 shows a conventional capacity control valve control apparatus disclosed in PTL 1. As shown in FIG. 8, the control apparatus includes pulse width modulation (PWM) converter 52 that controls capacity control valve 51 by using a duty ratio, and input voltage limiter circuit 53 that limits a voltage for setting a current that is input into pulse width modulation (PWM) converter 52.
With this configuration, pulse width modulation (PWM) converter 52 that generates a pulse signal having a predetermined duty ratio receives an input of a voltage indicating the predetermined duty ratio that is limited in advance by input voltage limiter circuit 53. For this reason, even if a voltage that excessively increases the pressure at the discharge side of the compressor is set, a pulse signal having a duty ratio greater than or equal to the predetermined duty ratio is not input into capacity control valve 51. Accordingly, it is possible to avoid a rapid pressure increase that may occur at the time of activation of the compressor.
Another capacity control valve control apparatus has also been proposed that limits the scalar value of a voltage applied to an electric motor provided in a compressor to be less than or equal to a maximum output voltage so as to effectively reduce a harmonic component of an input current (see, for example, PTL 2).
FIG. 9 shows a conventional compressor driving device disclosed in PTL 2.
As shown in FIG. 9, the compressor driving device includes rectification means 61 that rectifies an AC voltage from an AC power supply to a DC voltage, power conversion means 62 that converts the DC voltage output by rectification means 61 to an AC voltage and applies the AC voltage to the electric motor, phase current detectors 63a and 63b that detect phase currents flowing into the electric motor, and control means 64 that controls the voltage applied to the electric motor by power conversion means 62.
Control means 64 includes current control means 65 that receives a current command value of current flowing into the electric motor and outputs a voltage command value of the voltage applied to the electric motor based on the current command value, and output voltage limiting means 66 that limits the scalar value of the voltage applied to the electric motor to be less than or equal to the maximum output voltage that is defined by the DC voltage output by rectification means 61.
Current control means 65 includes an integrator. Current control means 65 calculates the voltage command value by performing a control operation including integral control by using the integrator based on the current command value and the outputs of phase current detectors 63a and 63b. 
Output voltage limiting means 66 receives the voltage command value from current control means 65, calculates the scalar value of the voltage command value, and limits the voltage applied to the electric motor if the scalar value exceeds the maximum output voltage defined by the DC voltage output by rectification means 61. Also, output voltage limiting means 66 feeds back the amount of limited voltage to current control means 65. Current control means 65 subtracts the amount of limited voltage that has been fed back from output voltage limiting means 66 from the output of the integrator.